Abstract:
Gestational age (GA) estimation is an important aspect of routine obstetrics scanning. Fetal parameters like femur length, biparietal diameter head circumference and abdominal circumference have many pit falls especially as pregnancy advances in age. Hence, there is need to estimate GA with placental thickness especially in the second and third trimesters when other fetal parameters may not be reliable. The aim of this study was to assess placental thickness as a sonographic index for estimating GA in the second and third trimester and thus determine the normal range of values of placental thickness. It was also aimed at determining if there is a racial difference in placental thickness. Six hundred and twenty seven (627) pregnant women with GA between 14 and 41 weeks were studied prospectively by ultrasound. Aloka Prosound 350 plus ultrasound machine with 3.5MHZ sector probe was used to scan the subjects. The placental thickness was obtained by measuring the anterior posterior diameter of the placenta at the level of insertion of the umbilical cord in a transabdominal longitudinal scan. The last menstrual period (LMP) of the women were recorded and fetal parameters which include FL, BPD, HC and AC were also measured and all of them were used to estimate the GA. There was a good positive relationship between GA and placental thickness (r = 0.910). Reference graph and tables for estimating GA using placental thickness were obtained. Placental thickness increases in a fairly linear manner as GA increases. A maximum mean placental thickness of 42 ± 2.9mm was recorded at 39weeks. There was a significant statistical difference between the results of this study when compared with previous work done in the Indian population (p < 0.05). This difference was not noted in similar work done in Nigeria. There was a high positive relationship between placental thickness and FL (r = 0.994), BPD (r = 0.993), HC (r = 0.960) and AC (r = 0.995). Regression analysis yielded this equation PT = 8.494 + 0.177FL + 0.172BPD + 0.001HC + 0.083AC which shows the relationship between placental thickness and the fetal parameters. Results suggest that placental thickness may be used to estimate GA in the second and third trimesters when other fetal parameters may not be reliable.
